Method and apparatus for manufacturing spherical metallic vessels or hemispherical vessel heads

ABSTRACT

A spherical container or a hemispherical head for a pressure vessel, is formed integrally of deposited weld metal. A first turntable is rotatable about a substantially horizontal axis which constitutes one diameter of the sphere, and a second turntable is rotatable about a substantially vertical axis which constitutes another diameter of the sphere perpendicular to the first diameter. A small spherical metallic segment constitutes a starting piece, and has a wall thickness equal to that of the vessel to be formed, the segment forming the base of a solid central angle of the sphere.

United States Patent Ujile [451 Dec. 26, 1972 54 METHOD ANDYAPPARATUS FOR MANUFACTURING SPHERICAL METALLIC VESSELS OR HEMISPHERICAL VESSEL HEADS [72] Inventor: Akira Ujile, Kobe, Japan- [73] Assignee: Mitsubishi Jukogyo Kaisha, Tokyo, Japan 22 Filed: March 26,1970 211 Appl. No.: 22,772

Int. Cl. ..B23k 9/04 [58] Field of Search ..219/76, 73,137

Kabushlkl [56] References Cited UNITED STATES PATENTS 1,533,300 4/1925 Bnken, 219/76 1,709,729 4/1929 Landgraf et a1. ..219/76 Primary Examiner-J. V. Truhe Assistant Examiner-J. G. Smith Attorney-MG1ew and Toren [5 7] ABSTRACT A spherical container or a hemispherical head for a pressure vessel, is formed integrally of deposited weld metal. A first turntable is rotatable about a substantially horizontal axis which constitutes one diameter of the sphere, and a second turntable is rotatable about a substantially vertical axis which constitutes another 'diameter of the sphere perpendicular to the first diameter. A small spherical metallic segment constitutes a starting piece, and has a wall thickness equal to that of the vessel to be formed, the segment forming the base of a solid central angle of the sphere.

3 Claims, 4 Drawing Figures METHOD AND APPARATUS FOR MANUFACTURING SPI-IERICAL METALLIC VESSELS OR HEMISPIIERICAL VESSEL I'IEADS BACKGROUND OF THE INVENTION tors, segments and the like, are joined toform the l spherical vessel. In manufacturing large-size spherical vessels, the spherical shells are divided into relatively small pieces which are then pressed into the required spherical form and joined together, as by welding.

In these conventional methods, relatively massive dies are required for bending plates, in bending presses, or by explosive formation, with the plates subsequently being welded to-each other. Consequently, these con- .ventional methods are costly and have disadvantages such as the increase in welding costs with the number of parts to be weld united, and the difficulty in controlling distortion. In addition, extensive use of high tension steel and other special steels, in recent years, has increased the difficulty of press-forming blank plates into spherical form.

SUMMARY OF THE INVENTION This invention relates to the manufacture of metallic vessels whose form constitutes at least a part of a sphere and, more particularly, to an improved method and apparatus for forming such vessels'in one piece substantially entirely by weld metal deposition.

The invention is based on the concept that it is possible to cover the entire surface of a spherical sell by means of a rope having a certain cross-sectional area, by dangling the rope from a vertex on the spherical shell and then swirling the rope. Base upon this concept, a spherical metallic structure is formed, with a vertex or pole thereof takenas a center, by replacing a unit volume of the rope with successively deposited weldmetal.

The method of the present invention is very effective inmanufacturing spherical pressure vessels, such as pressure vessels for use in petroleum refining, pressure vessels for chemical use, hemispherical ends for cylindrical pressure vessels for use in the atomic energy industry, superhigh pressure vessels for the atomic energy industry, and pressure vessels to be subjected to high external pressure, such as deep sea structures, or the like.

In accordance with the invention, a small spherical metallic segment is rotated about a horizontal axis which is a diameter of the spherical shell body of which the vessel forms at leasta part, as by being mounted symmetrically on a turntable, while progressively depositing and solidifying weld metal in the form of a continuous strip of weld metal along the peripheral edge of the segment and in the form of superposed convolutions whose width is substantially equal to the wall thickness of the vessel to be formed. The rate of rotation is coordinated with the rate of weld metal deposition to maintain a substantially uniform thickness of the deposited strip of weld metal. The point of weld metal Preferably, the periphery of the segment is formed with a tapered step portion extending completely therearound and having a maximum height equal to the thickness of the deposited strip of weld metal and a minimum height which is zero, the maximum and minimum heights coinciding to form a relatively abrupt step. A channel-shape mold embraces the periphery of the segment to receive the deposited weld metal'and Q flux, the weld deposition being effectedby electro-slag welding apparatus which is revolved at a rate coordinated with the progressive change in diameter of the vessel being formed.

An object of the invention is to provide an improved and simplified method for forming integral or onepiece metallic vessels whose form constitutes at least a part of a sphere.

Another object of the invention is to provide an im-' proved and simplified apparatus for performing the method.

A further object of the invention is to provide such a method and apparatus utilizing, as a starting piece for the vessel, a small spherical metallic segment forming the base of a solid central angle of the sphere and having a wall thickness equal to that of the vessel to be formed.

Another object of the invention is to provide such a method and apparatus in which such segment is rotated about an axis of symmetry which is a diameter of the sphere.

A further object of the invention is to provide such a method and apparatus in which, during rotation of the segment, a continuous strip of weld metal is progressively deposited along the peripheral edge of the segment in the form of superposed convolutions.

Another object of the invention is to provide such a method and apparatus in which the rate of rotation of the segment is coordinated with the rate of weld metal deposition to maintain a substantially uniform thickness of the deposited strip of weld metal.

A further object of the invention is to provide such a method and apparatus in which the point of weld metal deposition is revolved about an axis perpendicular to the axis of rotation of the segment and at a rate coordinated with the progressive change in diameter of the vessel being formed.

For an understanding of the principles of the invention, reference is made to the following description of a typical embodiment thereof as illustrated in the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 is a front elevation view, partly in section and partly schematic, illustrating apparatus embodying the invention;

FIG. 2 is a somewhat schematic plan view for explaining the principles of the invention;

FIG, 3 is a perspective viewof a vessel produced by the method and apparatus of the invention, during the course of production; and

FIG. 4 is a top plan view of the apparatus shown in FIG. I.

DESCRlPTION OF THE PREFERRED EMBODIMENT Referring first to FIGS. 1 and 4, a supporting base 1 supports a drive motor 2 driving a pinion 3 meshing with a drive gear 4 secured to a turntable 5, gear 4 and table 5 being rotatable about a substantially horizontal axis which constitutes a diameter HL of a sphere.

The parts used in the method and apparatus of the invention include a preformed work piece 7 in the form of a small spherical metallic segment forming the base of the solid central angle of the sphere and whose apex is at the center of the sphere, the work piece 7 having a wall thickness equal to that of the vessel to be formed. The apparatus further includes means for rotating work piece 7 about the horizontal axis HL, and including base 1, motor 2, pinion 3, gear 4 and turntable 5. In addition, the apparatus includes a means for forming substantially the entire surface of a spherical volume bounded by a spherical shell, with deposited weld metal wound" in a swirl from a vertex or pole of the spherical shell. I The starting piece 7, which is shown in FIG. 3 in perspective form, is mounted on turntable 5 by a bolt 6. The weld metal isdeposited onto starting piece 7 as if the weld metal were a rope having a cross section A defined by the spherical angle W, as represented by the shaded portion in explanatory FIG. 2.

The apparatus comprises three elements which will be described with reference to a vertical axis CL and a horizontal axis HL which intersect at the center G of a sphere of which the vessel to be formed constitute at least a part. In the first element, a starting block 7 mounted on a turntable 5 by a bolt 6 and weld metal, which has already been deposited on the starting block 7 to form part of the spherical product, are rotated by a motor 2 about the horizontal axis HL, the drive of motor 2 being applied to a driving gear 4 and a pinion 3. The second element is a weld deposit forming mechanismincluding a pulley on which is secured, for rotation with the pulley, an arm 8 having a length substantially equal to the inner radius of the sphere, pulley l0 swinging arm 8 through substantially 180 around the center G in order to orbit a mold 9 about center G. This mechanism extends from the exterior through an opening 31 diametrically opposite the bolt 6, and pulley 10 is rotatably supported on supporting members 11 and 12 in turn fixably supported by an upright shaft 13. Pulley 10 is rotated by means of a belt 14 extending through hole 31 and rotated by a pulley 15 secured to a shaft 17, outside the sphere, with shaft 17 being rotated by a motor 18.

The third element comprises a turntable 22, to which is secured a pulley 20, turntable 22 being rotatable about a vertical axis which is the diameter CL, and being supported above the work piece by a lateral arm 21 of upright or shaft 13, arm 21 terminating in an upwardly directed end 23 which forms the bearing for rotation of turntable 22. Turntable 22 supports feeding rollers 24 for the welding rod or wire 26 which is withdrawn from a reel 25 also supported on turntable 22. Welding current is supplied to welding rod or wire 26 by current contact shoe means 27 connected to one terminal of a welding power supply 30, another terminal of power supply 30 being connected to turntable 5.

Welding flux is supplied to backing member 9 by a conduit 29 leading from a flux hopper 28. A belt 19 connects pulley 20 for driving a pulley 16 secured to the shaft 17, so that turntable 22 is rotated in synchronism with arm 8.

The manner of operation of the apparatus will now be described. A blank 7, which can also be termed a starting block is formed inthe shape of spherical segment, as best seen in FIG. 3. Blank 7 may either be formed from deposited weld metal or may be machined from a steel plate which has been pressed into the shape of a small spherical segment. The peripheral edge of blank or starting block 7 is formed with a stepped portion having the cross sectional area indicated at A in FIG. 2. At its maximum height, the cross sectional area A of the stepped portion has an angular extent ya, at a point from its maximum height, the area A has an angular extent of half 'y() and, at the terminal or 360, the area A has an angular extent of zero. In effect, the peripheral edge of blank 7 is provided with a wedge extending through 360.

To start the operation of forming the spherical body, starting block 7 is mounted on turntable 5 by means of bolt 6, with the step A being horizontally oriented. Flux is fed from hopper 28 through conduit 29 into the substantially box-shaped receiver formed by step A, the mold 9, and the edge of starting block 7. Welding rod 26 is inserted into the flux, being fed by rollers 24 past the current contact jaws 27, which latter may be in the form of guide rollers. When a potential is applied between welding rod 26 and turntable 5, metallically connected to starting block 7,'an electro-slag welding procedure is initiated andthe mentioned box-shape receiver is filled with deposited weld metal. At the same time, the welding current penetrates into the step A and into the edge of starting block-7.

Motor 2 is then energized to rotate turntable 5, through gears 3 and 4, at an angular velocity such that the peripheral speed of blank 7 is coordinated with the rate of weld metal deposition along the periphery of starting block 7. The peripheral speed is maintained constant even with increasing diameter of the vessel being formed, and is determined by the thickness of the continuous strip of deposited weld metal which, in turn, is equal to the height of step A.

Simultaneously, motor 18 is energized to swing arm 8 and turntable 22 about the axis CL extending through the center G, and the rate of swinging effected by motor 18 is coordinated with the progressive change in diameter of the vessel being formed.

Thus, as the welding proceeds with the size of the spherical vessel increasing, the mold 9 is maintained always in contact with the periphery of the vessel, it being noted that after one complete revolution the starting block 7, the mold member 9 is in contact with the deposited continuous strip of weld metal. Furthermore, and due to rotation of turntable 22, the welding flux is always supplied to the welding point despite the increasing diameter or size of the vessel being formed.

Thus, by utilizing the method and apparatus of the invention, an integral or unitary spherical vessel is formed by depositing weld metal to surround the volume of a sphere in the manner of a swirl. The manner of depositing weld metal is analogous to the swirling of a rope having the cross sectional area A,

although the swirling of a rope would merely define a hollow space whereas the deposit of weld metal forms a solid body.

In the final stage of the method, the welding opera tion is terminated just before arm 8 completes a 180 swing in a horizontal plane including the diameter HL. The part 31 is left as an unfinished opening, so that the components of the welding apparatus can be withdrawn through this opening. In order that opening 31 be as small as possible, the components of the welding apparatus which are disposed inside the sphere are designed for disassembly for withdrawal. After withdrawal of these components through opening 31, a nozzle, a cover or the like may be inserted into opening 31 and welded to the remainder of the vessel to complete the formation of the vessel.

if an arm 32 is positioned behind arm 8, as shown in FIG. 4, and supports grinding means at its free end, finishing of the interior of the sphere can be effected simultaneously with the formation of the sphere by depositing weld metal.

From the foregoing, it will be noted that the invention has advantages such as eliminating bending operations, heating operations required for the bending operations, machining for edge preparation, which latter is very difficult to accomplish by a machine tool in the case of spherical elements so that manual machining usually is used, which increases the manufacturing cost, and other advantages. In addition, thick plates are not required to form the spherical vessel so that spherical vessels having thick walls can be manufactured substantially in one piece by using welding rods having the cross sectional area of thin plates such as, for example, flat elongated bars having a rectangular or polygonal cross section. Thereby, not only is therea reduction in the manufacturing costbut also spherical vessels of uniform :and excellent quality can be manufactured by using only deposited weld metal, through the application of the electro-slag remelting procedure which is the equivalent of vacuum melting, as in the case of slag melting. The accuracy of sphericity of the formed vessels is very high. Furthermore, vessels of different sizes can be manufactured using the same apparatus by merely changing the size of the mold 9 and changing the several jigs, such as the arm 8 and the like. In addition, if the operation is stopped at the equator, thus forming only half a sphere, the method is applicable to the formation of hemispherical ends for pressure vessels.

While a specific embodiment of the invention has been described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles.

What is claimed is:

1. A method of manufacturing metal vessels whose form constitutes at least a part of a sphere, comprising the steps of engaging a channel-shape mold with the edge of a small spherical metallic segment at a step portion of the segment maintained substantially on a horizontal plane, the segment forming the base of a solid central angle of the sphere whose apex is at the center of the sphere, the segment having a wall thickness substantially equal to that of the vessel to be formed and the ste ortion e tendin thr u h 360 and having a maxim im i step height sub stanti aIFy equal to the thickness of a strip of weld metal to be deposited on the edge of the segment and having a minimum height of zero, whereby to form a step for the initial deposition of weld metal; rotating the segment about a horizontal axis which is a diameter of the spherical shell of the vessel to be formed, in sliding engagement with the mold which is maintained substantially in a horizontal plane; during such rotation, progressively depositing a continuous weld metal strip, whose width is substantially equal to the wall thickness of the vessel to be formed, obtained by melting and solidifying electrode materials at a mold part, by the electroslag remelting procedure, the deposition being effected along a peripheral edge of the segment in the form of superposed convolutions; coordinating the rate of such rotation with therate of weld metal deposition to maintain a substantially uniform thickness of the deposited strip of weld metal; and swinging the mold about an axis perpendicular to the first-mentioned axis at a feed speed coordinated with the progressive change in diameter of the spherical shell that is being formed, and along the circumference of a circle which isin the same plane as the axis of rotation, which is the axis of symmetry, of the segment forming a starting block, while supporting the mold on an arm having a length equal to the inner radius of the spherical shell to be formed, in order to hold the mold initially in contact with the peripheral edge of the segment during the first complete rotation of the segment and thereafter in contact with the deposited and solidified weld metal strip constituting the peripheral edge of the spherical shell that is under formation, during succeeding rotations of the segment.

2. A method of manufacturing metallic vessels, as claimed in claim 1, including continuing deposition and solidification of such continuous weld metal strip until the vessel has the form of a sphere of solid metal, which sphere is complete except for an opening concentric with such horizontal axis which is a diameter of the spherical shell; then discontinuing formation of the continuous weld metal strip and withdrawing the mold and its support arm from the interior of the vessel through such opening; and thereafter inserting a vessel component into such opening and weld uniting the component to the essentially completely spherical vessel.

3. A method of manufacturing metallic vessels, as claimed in claim 1, including the step of progressively finish machining the interior of the vessel as the vessel is being formed. 

1. A method of manufacturing metal vessels whose form constitutes at least a part of a sphere, comprising the steps of engaging a channel-shape mold with the edge of a small spherical metallic segment at a step portion of the segment maintained substantially on a horizontal plane, the segment forming the base of a solid central angle of the sphere whose apex is at the center of the sphere, the segment having a wall thickness substantially equal to that of the vessel to be formed and the step portion extending through 360* and having a maximum step height substantially equal to the thickness of a strip of weld metal to be deposited on the edge of the segment and having a minimum height of zero, whereby to form a step for the initial deposition of weld metal; rotating the segment about a horizontal axis which is a diameter of the spherical shell of the vessel to be formed, in sliding engagement with the mold which is maintained substantially in a horizontal plane; during such rotation, progressively depositing a continuous weld metal strip, whose width is substantially equal to the wall thickness of the vessel to be formed, obtained by melting and solidifying electrode materials at a mold part, by the electroslag remelting procedure, the deposition being effected along a peripheral edge of the segment in the form of superposed convolutions; coordinating the rate of such rotation with the rate of weld metal deposition to maintain a substantially uniform thickness of the deposited strip of weld metal; and swinging the mold about an axis perpendicular to the first-mentioned axis at a feed speed coordinated with the progressive change in diameter of the spherical shell that is being formed, and along the circumference of a circle which is in the same plane as the axis of rotation, which is the axis of symmetry, of the segment forming a starting block, while supporting the mold on an arm having a length equal to the inner radius of the spherical shell to be formed, in order to hold the mold initially in contact with the peripheral edge of the segment during the first complete rotation of the segment and thereafter in contact with the deposited and solidified weld metal strip constituting the peripheral edge of the spherical shell that is under formation, during succeeding rotations of the segment.
 2. A method of manufacturing metallic vessels, as claimed in claim 1, including continuing deposition and solidification of such continuous weld metal strip until the vessel has the form of a sphere of solid metal, which sphere is complete except for an opening concentric with such horizontal axis which is a diameter of the spherical shell; then discontinuing formation of the continuous weld metal strip and withdrawing the mold and its support arm from the interior of the vessel through such opening; and thereafter inserting a vessel component into such opening and weld uniting the component to the essentially completely spherical vessel.
 3. A method of manufacturing metallic vessels, as claimed in claim 1, including the step of progressively finish machining the interior of the vessel as the vessel is being formed. 